1. Field of the Invention
The present invention relates to a seamable press felt for a machine for the production and/or processing of a fibrous material web, for example a paper, cardboard or tissue web, as well as to a method for its manufacture.
2. Description of the Related Art
Press felts normally consist of a tensile load accommodating carrier structure which also essentially provides the dimensional stability of the press felt. The carrier structures of current seamable press felts are often woven on a circular loom, whereby the machine direction threads are reverse woven, thereby forming seam loops. The disadvantage of structures which are woven on circular looms is that the circular weaving process is time intensive and expensive. Furthermore, the length of such carrier structures is limited to the width of the weaving loom utilized in the weaving process, since the warp threads represent the cross machine direction threads and the weft threads represent the machine direction threads.
In order to replace expensive circular weaving, the state of the art known from WO89/12717 suggests seamable press felts with flat woven carrier structures. With these press felts, the flat woven fabric is laid onto itself thus forming turned over edges, whereby cross direction threads are removed from the woven fabric in the area of the turned over edges. In this case, the machine direction threads of the woven fabric provide the seam loops of the seamable press felt in the area of the turned over edges. The process described in WO89/12717 permits simple manufacture of woven fabrics which are then fabricated to the appropriate dimensions for the press felt which is to be produced.
Especially in press felt applications there has been a long felt need to replace the woven fabrics, which are expensive to produce, with laid structures and/or knitted structures, since laid or knitted structures can be produced faster (often at 10 times the speed) compared to woven structures.
It is known from EP0261488 to construct the carrier structure of a press felt from a flat manufactured warp knit structure and to lay the structure onto itself thereby forming turned over edges, analog to the method cited in WO89/12717. However, in EP0261488 the seam loops are provided by means of additional wire spirals which are attached to the warp knit fabric structure in the area of the turned over edges. Due to this arrangement, the structure of the press felt in the seam area presents a considerable unevenness compared to the rest of the press felt, which can lead to vibrations during the operation of such press felts and marking of the paper produced on these press felts.
What is needed in the art is a press felt whereby a seam can be produced in the machine and which has a non-marking carrier structure that is inexpensive to produce.